Laminates comprising plasticized polyvinyl butyral interlayers

ABSTRACT

In a polyvinyl butyral (PVB) sheet plasticized with a multiester of an alcohol having 2 to 4 hydroxyl groups and a C 16  to C 20  unsaturated fatty acid having a hydroxyl group attached to the acid molecule, which sheet does not craze polycarbonate or polyacrylate when in contact therewith, the addition of a synergistically effective amount of a monoester of a glycol and such C 16  to C 20  acid improves the low temperature penetration resistance and adhesion properties of such sheet without significant loss in its resistance to stress cracking polycarbonate or polyacrylate in a laminated glass assembly.

BACKGROUND OF THE INVENTION

This invention relates to polyvinyl butyral (PVB) sheet plasticized withfatty acid esters and more particularly with a fatty acid ester blendwhich provides the sheet with improved penetration resistance withoutsignificant loss in its resistance to stress cracking polycarbonate orpolyacrylate when in contact therewith as an interlayer in a laminatedglass assembly.

In recent years sociologists and psychologists have started a movementtoward prisons without bars. Thick layers of impact resistantpolycarbonate initially used in such applications were quite earlydetermined to be inadequate since the polycarbonate could be burned orscratched or dissolved or fractured when heated or abused. Moreover,when exposed to the elements the polycarbonate turned yellow, lost itsstrength and was susceptable to crazing. Based on this early work a needwas defined for a material for security applications which was strong,chemically impervious, and scratch and fracture resistant over a widerange of ambient conditions.

Thereafter laminates of one or more layers of glass with one or morelayers of polycarbonate were proposed which in use were mounted with theglass layer on the outside exposed to the elements and the polycarbonateeither forming the innermost surface or positioned inboard of a glasslayer forming such innermost surface. However, with these laminates aninterlayer between the glass and polycarbonate is necessary sincepolycarbonate will not adequately adhere to glass.

Thermoplastic polyurethane layers have been used to laminatepolycarbonate to glass but polyurethanes are costly and usually requiretreatment of the glass with a primer coating before lamination.Moreover, such polyurethanes are difficult to process into laminatesbecause their low melting temperatures dictate the need for a batch typedeairing operation with long exposure to vacuum for complete airremoval. Commercially available grades of PVB sheet are not acceptableas an interlayer to adhere polycarbonate to glass because theplasticizer in the PVB crazes the polycarbonate. To solve this a specialbarrier coating, as disclosed in U.S. Pat. No. 4,243,719, was proposedbetween the polycarbonate and PVB to keep the plasticizer in the PVBaway from the polycarbonate. The PVB is still necessary since thecoating will not adhere to the glass and the PVB assists in absorbingenergy on impacting. Such a coating must be pinhole-free for obviousreasons and moreover is costly in that it represents an additional layerin an already multilayered laminate which could be avoided if aplasticizer for PVB were available which did not craze thepolycarbonate.

Sulfonamide and phosphate plasticizers for PVB which do not attackpolycarbonate are disclosed in U.S. Pat. Nos. 3,539,442 and 3,406,086respectively but PVB containing such plasticizers can only bedifficultly extruded in forming sheet since they tend to decompose atextrusion conditions and degrade the PVB.

Certain esters which in natural form can be the major constituents ofcastor oil are proposed in U.S. Pat. No. 4,128,694 as plasticizers forPVB which neither craze polycarbonate or polyacrylate nor deteriorateduring extrusion of plasticized PVB. However, such interlayers exhibitrelatively high glass transition temperatures (Tg) at the usualplasticizer loadings and marginal peel adhesion to polycarbonate whichmeans the impact properties at low performance temperatures are alsomarginal. This has precluded the use of such interlayers in securityglass applications exposed to cold climates.

A need, therefore, exists in the art for a plasticized PVB sheet havingthe properties of those disclosed in U.S. Pat. No. 4,128,694, but whichhas a low Tg and higher peel adhesion and therefore improved lowtemperature performance properties when present as a functional PVBinterlayer in a security glass laminate. Higher peel adhesion (i.e.equal to or greater than 10 newtons per cm) is needed to maintainlaminate integrity during and after laminate impacting. However, veryhigh peel adhesion (i.e. equal to greater than 30 newtons per cm) canproduce laminate failure due to breakthrough when the laminate isimpacted. On the other hand, very low peel adhesion (i.e. less than 10newtons per cm) can produce delamination on impacting, e.g. along thelaminate edges.

SUMMARY OF THE INVENTION

Now improvements have been developed which overcome the aforementioneddeficiencies of the prior art.

Accordingly, it is a principal object of this invention to provide aplasticized PVB interlayer which is usable with polycarbonate and hasimproved performance properties over a wide range of temperatures in asecurity glass laminate.

Another object of this invention is to provide a laminate of plasticizedPVB in adherent contact with polycarbonate or polyacrylate which hasimproved peel adhesion and high penetration resistance at lowtemperatures.

A further object is to provide such a PVB interlayer which can belaminated on existing commercial laminating lines without alteringlaminating conditions.

Other objects of this invention will in part be obvious and will in partappear from the following description and claims.

These and other objects are accomplished in a laminate comprising atleast one sheet of thermoplastic resin selected from the groupconsisting of polycarbonate and polyacrylate laminated to PVB sheetplasticized with a multiester of an alcohol having 2 to 4 hydroxylgroups and a C₁₆ to C₂₀ unsaturated fatty acid having a hydroxyl groupattached to the acid molecule by providing the improvement whichcomprises, in property-improving combination with such multiester, asynergistically effective amount of an additional plasticizer in saidPVB sheet which is a monoester of a glycol and such C₁₆ to C₂₀unsaturated fatty acid. The monoester is preferably propylene 1,2 glycolpartially esterified with ricinoleic acid.

DESCRIPTION OF PREFERRED EMBODIMENTS

U.S. Pat. No. 4,128,694 discloses a plasticizer for PVB resin in theform of a specific fatty acid multiester of an alcohol having 2 to 4hydroxyl groups and a C₁₆ to C₂₀ unsaturated fatty acid having ahydroxyl group attached to the acid molecule. The term "multiester" asused herein means an ester formed by esterifying more than one hydroxylgroup of such an alcohol with such an acid. Such plasticizer in a PVBinterlayer does not attack polycarbonate or polyacrylate when present ina multiple panel safety or security glass laminate assembly. In thepresent invention, a monoester species of such specific fatty acidmultiester is combined with the latter to form a plasticizer blend forPVB which unexpectedly lowers the Tg of PVB plasticized therewith andincrementally improves the PVB interlayer penetration resistance andpeel adhesion to polycarbonate over that obtained using the fatty acidmultiester alone. Performance with polyacrylate is predicted to besimilar. The plasticizer blend of the present invention, therefore,comprises a multiester component (e.g. a triester) combined with amonoester glycol component, each component being derivable from the sameclass of unsaturated fatty acids.

The preferred multiester component of the plasticizer blend of thepresent invention is contained in castor oil which is a triglycerideester of fatty acids. It comprises a mixture of esters of glycerol withthe following acids, (the figure in parentheses being the approximateweight percent of esters formed from that acid): ricinoleic acid(89.5%), oleic acid (3.0%), linoelic acid (4.2%), stearic acid 1% anddihydroxy-stearic acid. Approximately 63.6% of the ricinoleate istriester, (glycerol triricinoleate) 31.1% diester and 5.1% themonoester. The latter level of monoester in castor oil is insufficientin itself to provide the improvement of the present invention. Othermultiesters found useful wherein one molecule of the esterifying acidhas reacted with each available hydroxyl of the alcohol are those basedon triethylene glycol, trimethylol propane and pentaerythritol.

The unsaturated fatty acid monoester found synergistically effective asan additional plasticizer in combination with the preferred castor oilin PVB sheet in property improving combination in a blend with themultiester referred to above is a monoester of a glycol and a C₁₆ to C₂₀unsaturated fatty acid having a hydroxyl group attached to the acidmolecule. The preferred monoester is propylene glycol 1,2monoricinoleate. Though not certain of the reason, it appears that theunreacted hydroxyl group immediately adjacent the acid linkage in themonoester plays an important function in the plasticizer blend insofaras improving the peel adhesion to polycarbonate or polyacrylate of PVBinterlayer plasticized therewith, as well as the penetration resistanceof glass laminates made up of layers of these materials.

The acids that may be used to form the multiester and monoesterplasticizer components of the blend of the present invention have from16 to 20 carbon atoms and include in addition to ricinoleic acid,(12-hydroxyoleic acid) other hydroxy-oleic acids with the hydroxyl grouplocated other than on the "12" carbon atom such as 6-, 8-, 14-, or16-hydroxy-oleic acid, 12-hydroxyelaidic acid and acids with the sameempirical formula with the hydroxyl located on other than the "12" atom.Also included are the corresponding variations of12-hydroxy-hexodec-9-enoic acid and 12-hydroxy-eicos-9-enoic acid.

A single acid may provide all the esterifying acid groups but usually amixture of unsaturated esterifying acids, are used, provided that theesterifying acids together provide at least one unsaturation and onehydroxyl group per molecule of plasticizer.

The amount of plasticizer blend to be used in the laminate interlayer ofthe invention should be from 10 to 55 parts per hundred parts of PVBresin (phr). The preferred amount is 20 to 50 phr and particularlypreferred is 30 to 40 phr.

The weight proportion of monoester to multiester in the plasticizerblend should be between about 1:1 to about 5:1. When castor oil is usedas the multiester, allowance may optionally be made for the minor levelof monoester therein in determining the total amount of monoester to beused in the blend. It is preferred that the monoester be present as themajor constituent of the plasticizer blend, i.e. present in amountgreater than the multiester. The most preferred proportion of monoesterto multiester is 2:1.

The monoesters of the present invention are commercially available fromCasChem Inc., Bayonne, N.J., 07002 under the registered trademarkFlexricin. The various grades of each used in the Examples following areidentified in the footnotes to Table 1.

In general, the polyvinyl acetal resins employed may be considered to bemade up, on a weight basis, of from 5 to 25 percent hydroxyl groups,calculated as polyvinyl alcohol, 0 to 4 percent acetate groups,calculated as polyvinyl acetate, and the balance substantially acetal.When the acetal is butyraldehyde acetal, the polyvinyl acetal resin willpreferably contain, on a weight basis, from 10 to 25 percent hydroxylgroups, calculated as polyvinyl alcohol and from 0 to 10 percent acetategroups, calculated as polyvinyl acetate, the balance being substantiallybutyraldehyde acetal.

The polycarbonate component may be any suitable sheet of polycarbonatesuch as disclosed in U.S. Pat. Nos. 3,028,365 and 3,117,019 and ispreferably prepared by reacting di(monohydroxyaryl)-alkanes withderivatives of carbonic acid such as phosgene and bischloro-carbonicacid esters of di(monohydroxy-aryl)-alkanes. Commercial polycarbonatesheeting is available from General Electric Company under the trademarkLexan.

Where the resin sheet is a polyacrylate this may be as an ester of alower aliphatic alcohol, such as butyl-, propyl-, ethyl-, or methylalcohol and acrylic-, methacrylic-, ethacrylic, propacrylic- orbutacrylic- acid. By far the most convenient is polymethyl methacrylate.

The plasticized interlayer of the invention can be used to make a simplelaminate with the interlayer in contact on at least one surface with apolycarbonate or a polyacrylate sheet. Usually one of the surfaces ofthe interlayer will be in contact with a different material such asglass.

For security glass it is usual to provide multiple layers, such as fouror more, comprising plasticized interlayers and polycarbonate orpolyacrylate layers and glass layers laminated together to formlaminates of from 1/2 inch up to several inches in thickness. For suchpurposes the construction usually comprisesglass/interlayer/polycarbonate or polyacrylate/interlayer/glass unitsmultiplied as appropriate.

The laminates produced using the plasticized interlayer of the inventionmay be treated to reduce light transmission by tinting one or more ofthe component layers or by suppling a metallized surface to one or moreof the layers. The treatment can be such as to produce a uniformreduction in light transmission over the whole sheet or perhaps in theform of a band or other form of localized effect.

Laminates formed according to the present invention are broadly usefulin any application requiring a safety glass assembly such as invehicular windshields, but are especially useful in securityapplications such as prisons without bars and installations requiring asomewhat lesser degree of security such as bank windows, cashier booths,jewelry counters and the like. Applications in which the laminates ofthe invention can be used are disclosed in U.S. Pat. No. 4,243,719, col.10, line 3 through col. 12, line 36, the content of which isincorporated herein by reference.

In addition to the plasticizers, the interlayers of the presentinvention may contain other additives such as dyes, ultraviolet lightstabilizers, salts to control adhesion and antioxidants and may, ifdesired, be treated with additives to improve laminating efficiency.

The invention is further described with reference to the followingexamples which are for illustration only and are not intended to implyany limitation or restriction on the invention.

EXAMPLES 1-9

Laminates of uncoated, general purpose high impact, glazing grade,polycarbonate (Lexan 9030) and PVB sheet were made using variousplasticizers according to the following procedure.

The PVB used contained 18 weight percent hydroxly groups (measured aspolyvinyl alcohol) and had a solution viscosity of 230-250 cps asdetermined by Kinemetic Viscometer, Cannon Fenske type (ASTM D-4445).The plasticizer(s) was added to the PVB resin and mixed either manuallyor with a low intensity laboratory mixer and allowed to sit overnight topromote absorption of the plasticizer by the resin. A sigma blade mixerwith steam for heating passing through the mixer jacket was then usedfor about ten minutes to melt and mix the resin and plasticizer and formmolten crumbs of plasticized PVB.

The crumbs of plasticized PVB were deposited in a frame and pressed intoblocks 35.5 cm by 40.6 cm of about 5 cm thickness. Slices of plasticizedinterlayer of about 0.75 mm thickness were cut from these blocks andseparated from each other via interposed plastic film, conditioned forabout one hour at 20 to b 35% relative humidity to control moisturelevel therein at 0.4 to 0.5 weight %.

Initially washed polycarbonate (0.32 cm to 0.62 cm thickness) sheets andlayers of commercially available float glass were used in assemblingeach laminate as follows: a slice of plasticized interlayer was placedon either side of the polycarbonate layer and then a layer of glassplaced against each layer of interlayer. The loosely assembled laminatewas pre-compressed at about 46.7 kg/cm² at temperatures of 100° C.-215°C. in conventional manner using a heated press, then air-autoclaved at93° C., 3.5 kg/cm² for one hour, 10 min., followed by 135° C. and 13kg/cm² for one hour after which the temperature was reduced to 38° C.for 20 min. whereupon the pressure was reduced to end the cycle.

Other laminates for peel adhesion testing were prepared using standardlaminating techniques familiar to those in the art except that anadhesive coated aluminum foil was substituted for one of the glasslayers and the glass and interlayer on the other side of thepolycarbonate was eliminated.

Values for the various properties presented in Table 1 following weredetermined according to the following procedures.

The glass transition temperature (Tg) of plasticized PVB was measuredusing a Rheometric Mechanical Spectrometer which is a rectangulartorsion test conducted in a nitrogen atmosphere at a constant frequency(1-hertz) and temperature.

Compatability of plasticizer and PVB resin as determined by the extentof exudation of the plasticizer from the resin after melt mixing wasvisually noted by the absence or presence and level of free plasticizereither on the surface of the plasticized resin or in the bowl of thesigma mixer.

Penetration resistance of the glass-polycarbonate-plasticized interlayerlaminates was measured by dropping a 2270 gm steel ball five times from2.4 m onto the laminate which had been pre-conditioned for two hours atthe temperature at which the test was run. The integrity of the sampleinsofar as the extent, if any, of delamination along the glass cracksbetween the polycarbonate and interlayer was visually noted after fivedrops. The term "good integrity" as used in Table 1 following means thatsome portion of the laminate, such as the edge area, had all componentsadhered together after testing.

Clarity of the autoclaved laminate as determined by haze level wasvisually noted.

Stress cracking of the polycarbonate by the plasticizer(s) used in theinterlayer was determined at 23° C. and 70° C. In this test the stressapplied to polycarbonate specimens was incrementally increased to 2000psi while a patch saturated with the plasticizer fluid was applied atthe point of maximum stress and the stress noted at which crackingoccurred. More specifically, injection molded polycarbonate coupons inthe form of beams about 2.54 cm wide were loaded for a specified time,e.g. 10 minutes, and then the patch saturated with the test plasticizerwas applied to the point of maximum stress for an additional timedepending on the temperature-i.e. 72 hours at 23° C. and 8 hours at 70°C.

Peel adhesion-two parallel grooves 4 cm apart were formed lengthwisethrough the aluminum foil and interlayer. The polycarbonate at one endof the laminate a few cms in from the end was scored and brokenperpendicular to the grooves. The outside edge of the aluminum foil andinterlayer on each side of the 4 cm strip was cut at the polycarbonatebreak. The foil, interlayer and cut polycarbonate were then clamped inthe test grips of an Instron tensile tester and the force required toseparate the foil and interlayer from the polycarbonate along thegrooves measured at room temperature. A range of 10 to 30 newtons/cm isdesired to provide the optimum balance of impact and delaminationresistance in the laminate.

The results obtained are set forth in the following Table 1.

                                      TABLE 1                                     __________________________________________________________________________                  Plasticizer                        Peel Ad-                                        Ratio                         hesion                                     Amount                                                                             monoester/                                                                          Penetration resistance  Newtons/                     Example                                                                            Plasticizer                                                                            (phr)                                                                              polyester                                                                           -10° C.                                                                        0° C.                                                                          23° C.                                                                         cm                           __________________________________________________________________________    1    Glycerol tri-                                                                          47.5 --    complete de-                                                                          complete de-                                                                          signifi-                                                                              8-9                               ricinoleate.sup.1,5 lamination                                                                            lamination                                                                            cant de-                                                                      lamination                                                                    in impact                                                                     area                                 2    Glycerol tri-                                                                          12.75                                                                              2.4:1 some delamin-                                                                         some delamin-                                                                         no delamina-                                                                          .sup. 15-22.sup.3                 ricinoleate (GT)                                                                       30         ation-good                                                                            ation-good                                                                            tion-good                                 and propylene       laminate in-                                                                          laminate in-                                                                          laminate in-                              glycol monori-      tegrity tegrity tegrity                                   cinoleate (PGM).sup.2,5                                                  3    Propylene glycol                                                                       42   --    significant                                                                             --    --      12                                monoricinoleate     delamination                                              (PGM)               in impact area-                                                               good laminate                                                                 integrity                                            4    Pentaerythritol                                                                        45   --      --      --    --      12.8                              Monoricinoleate.sup.4                                                    5    Glycerol triricin-                                                                     15   2.0:1   --      --    --      --                                oleate/pentaery-                                                                       30                                                                   thritol monoricin-                                                            oleate                                                                   6    Ethylene glycol                                                                        45         significant de-                                                                         --    --      13.6                              monoricinoleate.sup.6                                                                             lamination in                                                                 impact area;                                                                  good laminate                                                                 integrity                                            7    Glycol triricin-                                                                       15   2.0:1 some delamina-                                                                          --    --      10.5                              oleate/ethylene                                                                        30         ation in impact                                           glycol monoricin-   area; good lam-                                           oleate              inate integrity                                      8    Glycerol mono-                                                                         42.5 --      --    --      --      13.0                              ricinoleate                                                              9    Glycerol tri-                                                                          12.5 2.4:1 complete.sup.7                                                                        --      --      13.2                              ricinoleate/                                                                           30.0       delamina-                                                 glycerol            tion                                                      monoricinoleate                                                          __________________________________________________________________________                          Tg                  Stress Cracking (psi)                                Example                                                                            (°C.)                                                                        Compatibility                                                                          Clarity                                                                           23° C.                                                                        70° C.                 __________________________________________________________________________                     1    36-38 fair     good                                                                              None at 2000                                                                         None at 2000                                   2    17.5  good     good                                                                              None at 2000                                                                         1700                                           3    18    good     good                                                                              None at 2000                                                                         1000                                           4    30    fair     fair                                                                              None at 2000                                                                         None at 2000                                   5    >30° C.                                                                      fair     poor-                                                                             --     --                                                  (Estimated)    reddish                                                                       tinge                                                     6    19    good     good                                                                              None at 2000                                                                         1000                                           7    23    good     good                                                                              --     --                                             8    26    poor-    fair-                                                                             None at 2000                                                                         1500                                                      (over lubricated)                                                                      reddish                                                                       tinge                                                     9    26    poor-    fair                                                                              --     --                                                        (over lubricated)                                 __________________________________________________________________________     .sup.1 AA-Standard Grade Castor Oil from Spencer Kellogg                      .sup.2 PGM ws Flexricin 9                                                     .sup.3 Value of 22 obtained with cosmetic (pure) grade of Flexricin 9         .sup.4 Flexricin 17                                                           .sup.5 Laminates were 0.6 m by 0.6 m                                          .sup.6 Flexricin 15                                                           .sup.7 Laminates were 10 cm by 15 cm                                     

Stress crack performance of the glycerol triricinoleate/ethylene glycolmonoricinolate blend of Example 7 is predicted to be equivalent to thatobtained with the blend of Example 2 containing propylene glycolmonoricinoleate.

The foregoing data indicates that when the multiester is the sole orprincipal plasticizer in the plasticized interlayer (Example 1) inaccordance with U.S. Pat. No. 4,128,694, though stress crack resistanceof the polycarbonate is good, the tendency to delaminate is high andtherefore the penetration resistance is poor because of the relativelyhigh value of Tg and low peel adhesion. When the lower molecular weightglycol monoester (Examples 3 and 6) was used alone, Tg was reduced andpentration resistance was improved, but at the expense of stress crackresistance of the polycarbonate at high temperature. However, when onlya relatively minor amount (12.5-15 parts) of the multiester was added tothe monoester, (Examples 2, and 7) acceptable stress crack resistancewas obtained and peel adhesion was significantly increased with respectto the propylene glycol monoricinoleate species of Example 2 without areduction in Tg and in penetration resistance. This significant increasein peel adhesion and failure of Tg to increase with the addition of themultiester constituent to the monoester constituent was unexpected. Theblend containing a monoester of an alcohol having more than two hydroxylgroups, i.e. the pentaerythritol monoricinoleate species of Example 5and the glycerol monoricinoleate species of Example 9, which are outsidethe scope of this invention, were deficient in color (Example 5) andcompatibility (Example 9).

Though the plasticized PVB sheet of the invention can be formed byslicing from blocks as disclosed in the foregoing Examples, it ispreferably formed by extrusion mixing and sheet formation of theinterlayer in a slot die.

The monoester glycol component of the plasticizer blend of the inventionmay comprise blends of monoesters, such as a blend of individualethylene and propylene glycol monoester constituents.

While certain specific embodiments of the invention have been describedwith particularity herein, it will be recognized that variousmodifications thereof will occur to those skilled in the art. The scopeof the invention, therefore, is to be limited solely by the scope of thefollowing claims.

I claim:
 1. In a laminate comprising at least one sheet of thermoplasticresin selected from the group consisting of polycarbonate andpolyacrylate laminated to a polyvinyl butyral sheet plasticized with amultiester of an alcohol having 2 to 4 hydroxyl groups and a C₁₆ to C₂₀unsaturated fatty acid having a hydroxyl group attached to the acidmolecule, the improvement which comprises, in property improvingcombination with such multiester, a synergistically effective amount ofan additional plasticizer in said polyvinyl butyral sheet which is amonoester of a glycol and said C₁₆ to C₂₀ unsaturated fatty acid,wherein the ratio of said monoester to said multiester is between about1:1 to about 5:1.
 2. The laminate of claim 1 wherein the monoester ispropylene glycol-1,2 monoricinoleate.
 3. The laminate of claim 1 whereinthe monoester is ethylene glycol monoricinoleate.
 4. The laminate ofclaim 1 wherein said ratio is about 2:1.
 5. The laminate of claim 4wherein the thermoplastic resin is polycarbonate.
 6. The laminate ofclaim 5 wherein the multiester is present as castor oil.
 7. The laminateof claim 6 including at least one sheet of glass laminated to saidpolyvinyl butyral sheet.